The Liquid FX Emitter does not simulate a liquid of its own. Instead, it works in a similar way to the Reproduce emitter: It evaluates the particles of an existing liquid simulation, for example from a Liquid Flow Emitter or a Liquid Fill Emitter, and procedurally emits new particles from them. Where this happens is determined by physical quantities estimated for each liquid particle: Fast-moving, curved areas of the surface such as wave crests, and areas where air is trapped in the liquid, emit particles. The emitter takes into account all liquid particles within its Simulation Scene.

The new particles are managed in three separate Particle Groups, which are created automatically and linked to the emitter when you create it. This allows you to color, render, and process spray, foam, and bubbles independently of each other. Each type behaves differently:

• Spray: Particles with only a few liquid neighbors, for example drops that fly through the air. They simply move by inertia.
• Foam: Particles on the surface of the liquid. They are drifted by the surrounding liquid and stay at a specific offset from the surface.
• Bubbles: Particles inside the liquid. They are drifted by the surrounding liquid and additionally experience buoyancy, so they rise to the surface.

Note that a particle does not keep its type permanently. It is classified anew on every frame based on the number of surrounding liquid particles, and the exact values for this can be set on the Liquid tab of the Simulation Scene object. Spray that falls back into the liquid turns into foam or bubbles, for example, and bubbles that reach the surface turn into foam. This is why there is no separate amount setting for each particle type.

The settings of the emitter are divided into several tabs: The Emission tab determines from which liquid particles and how many new particles are emitted. The Properties tab defines how spray, foam, and bubbles behave and how long they exist. On the Output tab, you can store information such as newly created particles or their source liquid particle in custom properties. An overview of the settings that change the amount of each particle type can be found in the introduction to Liquid FX.

If you want to define yourself where spray, foam, or bubbles are created, use the Liquid FX Modifier instead. It converts the particles of any emitter directly into Liquid FX particles.

Examples of Use

Spray and foam for a splash: Create a liquid simulation, for example with a Liquid Flow Emitter whose jet hits a surface, and add a Liquid FX Emitter to the scene. Play the simulation from the first frame: Spray and foam are created mainly where the liquid splashes and forms wave crests. Use Resolution on the Emission tab to increase or decrease the number of all particles. To keep the spray visible for longer, lower its Lifetime Decay on the Properties tab while Limited is enabled. Work with a low Resolution while you adjust the settings, and raise it only for the final simulation.

Bubbles in turbulent liquid: If a liquid is poured into a container, air is trapped where the jet enters the liquid. The Trapped Air settings on the Emission tab create bubbles there, which rise and collect as foam at the surface. In fast-moving liquids, these settings can also add a lot of spray and foam. If no bubbles appear, the trapped air value of the liquid is probably below the Threshold; lower this value step by step. A higher Rate then increases the number of particles emitted from trapped air, independently of the settings for the wave crests.